/* ==========================================
 * JGraphT : a free Java graph-theory library
 * ==========================================
 *
 * Project Info:  http://jgrapht.sourceforge.net/
 * Project Creator:  Barak Naveh (http://sourceforge.net/users/barak_naveh)
 *
 * (C) Copyright 2003-2006, by Barak Naveh and Contributors.
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; if not, write to the Free Software Foundation,
 * Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 */
/* -------------
 * Subgraph.java
 * -------------
 * (C) Copyright 2003-2006, by Barak Naveh and Contributors.
 *
 * Original Author:  Barak Naveh
 * Contributor(s):   Christian Hammer
 *
 * $Id: Subgraph.java,v 1.2 2007/05/22 15:52:53 kjellw Exp $
 *
 * Changes
 * -------
 * 24-Jul-2003 : Initial revision (BN);
 * 26-Jul-2003 : Accurate constructors to avoid casting problems (BN);
 * 10-Aug-2003 : Adaptation to new event model (BN);
 * 23-Oct-2003 : Allowed non-listenable graph as base (BN);
 * 07-Feb-2004 : Enabled serialization (BN);
 * 11-Mar-2004 : Made generic (CH);
 * 15-Mar-2004 : Integrity is now checked using Maps (CH);
 * 20-Mar-2004 : Cancelled verification of element identity to base graph (BN);
 * 21-Sep-2004 : Added induced subgraph (who?)
 * 07-May-2006 : Changed from List<Edge> to Set<Edge> (JVS);
 * 28-May-2006 : Moved connectivity info from edge to graph (JVS);
 *
 */
package org.jgrapht.graph;

import java.io.*;

import java.util.*;

import org.jgrapht.*;
import org.jgrapht.event.*;
import org.jgrapht.util.*;

/**
 * A subgraph is a graph that has a subset of vertices and a subset of edges
 * with respect to some base graph. More formally, a subgraph G(V,E) that is
 * based on a base graph Gb(Vb,Eb) satisfies the following <b><i>subgraph
 * property</i></b>: V is a subset of Vb and E is a subset of Eb. Other than
 * this property, a subgraph is a graph with any respect and fully complies with
 * the <code>Graph</code> interface.
 * 
 * <p>
 * If the base graph is a {@link org.jgrapht.ListenableGraph}, the subgraph
 * listens on the base graph and guarantees the subgraph property. If an edge or
 * a vertex is removed from the base graph, it is automatically removed from the
 * subgraph. Subgraph listeners are informed on such removal only if it results
 * in a cascaded removal from the subgraph. If the subgraph has been created as
 * an induced subgraph it also keeps track of edges being added to its vertices.
 * If vertices are added to the base graph, the subgraph remains unaffected.
 * </p>
 * 
 * <p>
 * If the base graph is <i>not</i> a ListenableGraph, then the subgraph
 * property cannot be guaranteed. If edges or vertices are removed from the base
 * graph, they are <i>not</i> removed from the subgraph.
 * </p>
 * 
 * <p>
 * Modifications to Subgraph are allowed as long as the subgraph property is
 * maintained. Addition of vertices or edges are allowed as long as they also
 * exist in the base graph. Removal of vertices or edges is always allowed. The
 * base graph is <i>never</i> affected by any modification made to the
 * subgraph.
 * </p>
 * 
 * <p>
 * A subgraph may provide a "live-window" on a base graph, so that changes made
 * to its vertices or edges are immediately reflected in the base graph, and
 * vice versa. For that to happen, vertices and edges added to the subgraph must
 * be <i>identical</i> (that is, reference-equal and not only value-equal) to
 * their respective ones in the base graph. Previous versions of this class
 * enforced such identity, at a severe performance cost. Currently it is no
 * longer enforced. If you want to achieve a "live-window"functionality, your
 * safest tactics would be to NOT override the <code>equals()</code> methods
 * of your vertices and edges. If you use a class that has already overridden
 * the <code>equals()</code> method, such as <code>String</code>, than you
 * can use a wrapper around it, or else use it directly but exercise a great
 * care to avoid having different-but-equal instances in the subgraph and the
 * base graph.
 * </p>
 * 
 * <p>
 * This graph implementation guarantees deterministic vertex and edge set
 * ordering (via {@link LinkedHashSet}).
 * </p>
 * 
 * @author Barak Naveh
 * @see Graph
 * @see Set
 * @since Jul 18, 2003
 */
public class Subgraph<V, E, G extends Graph<V, E>> extends AbstractGraph<V, E>
		implements Serializable {
	// ~ Static fields/initializers
	// ---------------------------------------------

	private static final long serialVersionUID = 3208313055169665387L;

	private static final String NO_SUCH_EDGE_IN_BASE = "no such edge in base graph";

	private static final String NO_SUCH_VERTEX_IN_BASE = "no such vertex in base graph";

	// ~ Instance fields
	// --------------------------------------------------------

	//
	Set<E> edgeSet = new LinkedHashSet<E>(); // friendly to improve
												// performance

	Set<V> vertexSet = new LinkedHashSet<V>(); // friendly to improve

	// performance

	//
	private transient Set<E> unmodifiableEdgeSet = null;

	private transient Set<V> unmodifiableVertexSet = null;

	private G base;

	private boolean isInduced = false;

	// ~ Constructors
	// -----------------------------------------------------------

	/**
	 * Creates a new Subgraph.
	 * 
	 * @param base
	 *            the base (backing) graph on which the subgraph will be based.
	 * @param vertexSubset
	 *            vertices to include in the subgraph. If <code>
	 * null</code>
	 *            then all vertices are included.
	 * @param edgeSubset
	 *            edges to in include in the subgraph. If <code>
	 * null</code>
	 *            then all the edges whose vertices found in the graph are
	 *            included.
	 */
	public Subgraph(G base, Set<V> vertexSubset, Set<E> edgeSubset) {
		super();

		this.base = base;

		if (edgeSubset == null) {
			isInduced = true;
		}

		if (base instanceof ListenableGraph) {
			((ListenableGraph<V, E>) base)
					.addGraphListener(new BaseGraphListener());
		}

		addVerticesUsingFilter(base.vertexSet(), vertexSubset);
		addEdgesUsingFilter(base.edgeSet(), edgeSubset);
	}

	/**
	 * Creates a new induced Subgraph. The subgraph will keep track of edges
	 * being added to its vertex subset as well as deletion of edges and
	 * vertices. If base it not listenable, this is identical to the call
	 * Subgraph(base, vertexSubset, null) .
	 * 
	 * @param base
	 *            the base (backing) graph on which the subgraph will be based.
	 * @param vertexSubset
	 *            vertices to include in the subgraph. If <code>
	 * null</code>
	 *            then all vertices are included.
	 */
	public Subgraph(G base, Set<V> vertexSubset) {
		this(base, vertexSubset, null);
	}

	// ~ Methods
	// ----------------------------------------------------------------

	/**
	 * @see Graph#getAllEdges(Object, Object)
	 */
	public Set<E> getAllEdges(V sourceVertex, V targetVertex) {
		Set<E> edges = null;

		if (containsVertex(sourceVertex) && containsVertex(targetVertex)) {
			edges = new ArrayUnenforcedSet<E>();

			Set<E> baseEdges = base.getAllEdges(sourceVertex, targetVertex);

			for (Iterator<E> iter = baseEdges.iterator(); iter.hasNext();) {
				E e = iter.next();

				if (edgeSet.contains(e)) { // add if subgraph also contains
					// it
					edges.add(e);
				}
			}
		}

		return edges;
	}

	/**
	 * @see Graph#getEdge(Object, Object)
	 */
	public E getEdge(V sourceVertex, V targetVertex) {
		Set<E> edges = getAllEdges(sourceVertex, targetVertex);

		if ((edges == null) || edges.isEmpty()) {
			return null;
		} else {
			return edges.iterator().next();
		}
	}

	/**
	 * @see Graph#getEdgeFactory()
	 */
	public EdgeFactory<V, E> getEdgeFactory() {
		return base.getEdgeFactory();
	}

	/**
	 * @see Graph#addEdge(Object, Object)
	 */
	public E addEdge(V sourceVertex, V targetVertex) {
		assertVertexExist(sourceVertex);
		assertVertexExist(targetVertex);

		if (!base.containsEdge(sourceVertex, targetVertex)) {
			throw new IllegalArgumentException(NO_SUCH_EDGE_IN_BASE);
		}

		Set<E> edges = base.getAllEdges(sourceVertex, targetVertex);

		for (Iterator<E> iter = edges.iterator(); iter.hasNext();) {
			E e = iter.next();

			if (!containsEdge(e)) {
				edgeSet.add(e);

				return e;
			}
		}

		return null;
	}

	/**
	 * @see Graph#addEdge(Object, Object, Object)
	 */
	public boolean addEdge(V sourceVertex, V targetVertex, E e) {
		if (e == null) {
			throw new NullPointerException();
		}

		if (!base.containsEdge(e)) {
			throw new IllegalArgumentException(NO_SUCH_EDGE_IN_BASE);
		}

		assertVertexExist(sourceVertex);
		assertVertexExist(targetVertex);

		assert (base.getEdgeSource(e) == sourceVertex);
		assert (base.getEdgeTarget(e) == targetVertex);

		if (containsEdge(e)) {
			return false;
		} else {
			edgeSet.add(e);

			return true;
		}
	}

	/**
	 * Adds the specified vertex to this subgraph.
	 * 
	 * @param v
	 *            the vertex to be added.
	 * 
	 * @return <code>true</code> if the vertex was added, otherwise <code>
	 * false</code>.
	 * 
	 * @throws NullPointerException
	 * @throws IllegalArgumentException
	 * 
	 * @see Subgraph
	 * @see Graph#addVertex(Object)
	 */
	public boolean addVertex(V v) {
		if (v == null) {
			throw new NullPointerException();
		}

		if (!base.containsVertex(v)) {
			throw new IllegalArgumentException(NO_SUCH_VERTEX_IN_BASE);
		}

		if (containsVertex(v)) {
			return false;
		} else {
			vertexSet.add(v);

			return true;
		}
	}

	/**
	 * @see Graph#containsEdge(Object)
	 */
	public boolean containsEdge(E e) {
		return edgeSet.contains(e);
	}

	/**
	 * @see Graph#containsVertex(Object)
	 */
	public boolean containsVertex(V v) {
		return vertexSet.contains(v);
	}

	/**
	 * @see Graph#edgeSet()
	 */
	public Set<E> edgeSet() {
		if (unmodifiableEdgeSet == null) {
			unmodifiableEdgeSet = Collections.unmodifiableSet(edgeSet);
		}

		return unmodifiableEdgeSet;
	}

	/**
	 * @see Graph#edgesOf(Object)
	 */
	public Set<E> edgesOf(V vertex) {
		assertVertexExist(vertex);

		Set<E> edges = new ArrayUnenforcedSet<E>();
		Set<E> baseEdges = base.edgesOf(vertex);

		for (E e : baseEdges) {
			if (containsEdge(e)) {
				edges.add(e);
			}
		}

		return edges;
	}

	/**
	 * @see Graph#removeEdge(Object)
	 */
	public boolean removeEdge(E e) {
		return edgeSet.remove(e);
	}

	/**
	 * @see Graph#removeEdge(Object, Object)
	 */
	public E removeEdge(V sourceVertex, V targetVertex) {
		E e = getEdge(sourceVertex, targetVertex);

		return edgeSet.remove(e) ? e : null;
	}

	/**
	 * @see Graph#removeVertex(Object)
	 */
	public boolean removeVertex(V v) {
		// If the base graph does NOT contain v it means we are here in
		// response to removal of v from the base. In such case we don't need
		// to remove all the edges of v as they were already removed.
		if (containsVertex(v) && base.containsVertex(v)) {
			removeAllEdges(edgesOf(v));
		}

		return vertexSet.remove(v);
	}

	/**
	 * @see Graph#vertexSet()
	 */
	public Set<V> vertexSet() {
		if (unmodifiableVertexSet == null) {
			unmodifiableVertexSet = Collections.unmodifiableSet(vertexSet);
		}

		return unmodifiableVertexSet;
	}

	/**
	 * @see Graph#getEdgeSource(Object)
	 */
	public V getEdgeSource(E e) {
		return base.getEdgeSource(e);
	}

	/**
	 * @see Graph#getEdgeTarget(Object)
	 */
	public V getEdgeTarget(E e) {
		return base.getEdgeTarget(e);
	}

	private void addEdgesUsingFilter(Set<E> edgeSet, Set<E> filter) {
		E e;
		boolean containsVertices;
		boolean edgeIncluded;

		for (Iterator<E> iter = edgeSet.iterator(); iter.hasNext();) {
			e = iter.next();

			V sourceVertex = base.getEdgeSource(e);
			V targetVertex = base.getEdgeTarget(e);
			containsVertices = containsVertex(sourceVertex)
					&& containsVertex(targetVertex);

			// note the use of short circuit evaluation
			edgeIncluded = (filter == null) || filter.contains(e);

			if (containsVertices && edgeIncluded) {
				addEdge(sourceVertex, targetVertex, e);
			}
		}
	}

	private void addVerticesUsingFilter(Set<V> vertexSet, Set<V> filter) {
		V v;

		for (Iterator<V> iter = vertexSet.iterator(); iter.hasNext();) {
			v = iter.next();

			// note the use of short circuit evaluation
			if ((filter == null) || filter.contains(v)) {
				addVertex(v);
			}
		}
	}

	public G getBase() {
		return base;
	}

	/**
	 * @see Graph#getEdgeWeight(Object)
	 */
	public double getEdgeWeight(E e) {
		return base.getEdgeWeight(e);
	}

	/**
	 * @see WeightedGraph#setEdgeWeight(Object, double)
	 */
	public void setEdgeWeight(E e, double weight) {
		((WeightedGraph<V, E>) base).setEdgeWeight(e, weight);
	}

	// ~ Inner Classes
	// ----------------------------------------------------------

	/**
	 * An internal listener on the base graph.
	 * 
	 * @author Barak Naveh
	 * @since Jul 20, 2003
	 */
	private class BaseGraphListener implements GraphListener<V, E>,
			Serializable {
		private static final long serialVersionUID = 4343535244243546391L;

		/**
		 * @see GraphListener#edgeAdded(GraphEdgeChangeEvent)
		 */
		public void edgeAdded(GraphEdgeChangeEvent<V, E> e) {
			if (isInduced) {
				E edge = e.getEdge();
				addEdge(base.getEdgeSource(edge), base.getEdgeTarget(edge),
						edge);
			}
		}

		/**
		 * @see GraphListener#edgeRemoved(GraphEdgeChangeEvent)
		 */
		public void edgeRemoved(GraphEdgeChangeEvent<V, E> e) {
			E edge = e.getEdge();

			removeEdge(edge);
		}

		/**
		 * @see VertexSetListener#vertexAdded(GraphVertexChangeEvent)
		 */
		public void vertexAdded(GraphVertexChangeEvent<V> e) {
			// we don't care
		}

		/**
		 * @see VertexSetListener#vertexRemoved(GraphVertexChangeEvent)
		 */
		public void vertexRemoved(GraphVertexChangeEvent<V> e) {
			V vertex = e.getVertex();

			removeVertex(vertex);
		}
	}
}

// End Subgraph.java
